Maintenance of a viable airway is critical to patient safety during surgical procedures conducted under general anesthetic. Maintenance of a viable airway during such surgical procedures had, for many years, been achieved by insertion of an endo-tracheal tube into the patient. The endo-tracheal tube was typically inserted through the oral cavity or nasal cavity, into the larynx, through the vocal cord and into the trachea. As the endo-tracheal tube had to be inserted through the vocal cords, difficulty was often experienced in correctly positioning the endo-tracheal tube.
British patent no. 2,111,394 (which corresponds to U.S. Pat. No. 4,509,514) describes a device for maintaining an airway in a patient. The device is described as being an artificial airway device. The device comprises a curved, flexible tube opening at one end into the interior of a hollow mask portion shaped to conform to fit readily into the actual and potential space behind the larynx and to seal around the circumference of the laryngeal inlet without penetrating into the interior of the larynx. Commercial forms of this device have an inflatable collar extending around the periphery of the mask. The inflatable collar is adapted to form the seal around the laryngeal inlet when the collar is inflated. Additionally, the mask portion included an inflatable posterior part which is adapted to press against the back of the throat and thereby increase the sealing pressure around the laryngeal inlet.
British patent no. 2,111,394 states that the shape and (when fitted) the inflatable part or parts of the mask ensure that it approximates closely to the shape of the space between the laryngeal inlet and the walls of the lower part of the throat behind it. Since the walls of tissue forming the back of the throat are relatively rigid, inflation of the mask forces it more tightly against the tissues surrounding the laryngeal inlet, so forming an airtight seal, while tending to anchor the mask in position.
In use of the device described in GB 2,111,394, the device is inserted through the mouth of the patient and down the throat past the epiglottis until the mask comes to rest with its distal end in the base of the throat, lying against the upper end of the normally closed esophagus. The inflatable ring on the mask is then inflated to seal around the inlet to the larynx. The patent's airway in thus secure and unobstructed and the laryngeal mask can be connected directly to conventional anesthetic circuit hosing for either positive pressure or spontaneously breathing.
When a patient is placed under general anesthetic, the patient is frequently lying in the horizontal position on his or her back or side. When under general anesthetic, reflex response in the body is suppressed and the sphincter closing the top of the stomach from the esophagus is relaxed. Consequently, gastric juices (which are acidic in nature) can flow along the esophagus. It is important to ensure that such gastric juices do not enter the trachea as aspiration of gastric juices into the lungs can have potentially fatal consequences.
Similarly, where a patient under general anesthetic is undergoing a surgical procedure of the nose, mouth or throat (e. g. a tonsillectomy, endoscopic nasal surgery), saliva, blood and nasal secretions can travel down through the pharyngo larynx and into the trachea and thereafter into the lungs. Again, this is a potentially dangerous situation.
When using a laryngeal mask such as the one described in British patent no. 2,111,394, the present inventor has found that if significant volumes of gastric juices collect around the mask the gastric juices can work their way past the seal of the mask and into the larynx. This is dangerous if the gastric juices and acid gets into the lungs.
The laryngeal mask described in British patent no. 2,111,394 may also have problems of leakage occurring in the inflatable ring or collar, due to a faulty valve in the pilot line or due to leakage or tearing of the inflatable ring or collar. It is apparent that deflation of the cuff substantially increases the chance that the seal around the larynx will be lost, which consequently increases the possibility of gastric acids getting into the lungs. Even in normal use without cuff deflation, there remains a possibility that a gush of acid from the stomach can get around the cuff and enter the air passage as there is no other way for the acid to escape (due to the cuff totally blocking the laryngopharynx). The presently available masks also have the limitation that they cannot be used safely on all patients, especially patients with a large abdomen.
In order to minimize the likelihood of the abovementioned problems, the patentee of British patent no. 2,111,394 introduced a laryngeal mask that had a double cuff to produce a total seal around the area of the larynx. This mask also included an additional tube that extends along the back of the laryngeal mask and extends into the esophagus. This allows gastric acid to be sucked out from the stomach by way of a Ryles tube inserted through this passage. It has been found that applying suction to the esophageal tube of this laryngeal mask can cause the tissue of the esophagus to be sucked into the inlet of the second tube. This results in the second tube becoming blocked, thereby preventing removal of gastric acids.
The double cuff laryngeal mask also includes two small additional tubes that open into the larynx-side of the mask. These tubes can be used to remove from the larynx any gastric juices that make their way past the seal into the larynx.
However, applying suction to these tubes raises the possibility of removing anesthetic gases from the trachea and increases the possibility of collapsing the lung or lungs. Successful removal of all the volume of acid coming up from the stomach is also not possible. Consequently, the acid may preferably move into the large diameter airway (trachea) due to the large diameter of the airway providing a path of lower resistance to fluid flow than the smaller diameter opening in the mask.
The improved laryngeal mask described above is described in Australian patent no. 630433. Despite those improvements, further enhancements and modifications are needed, and these are now provided by he present invention.